Modern computer processor chips have an idle mode such that the processor shuts down when not in use. This minimizes the power consumption and heat dissipation and may prolong the life of the processor chip. Once asleep, there must be some mechanism to wake the processor chip. Preferably, the processor system will instantaneously wake up when needed. In order to accomplish this goal, various portions of the system must stay awake while others are sleeping. To operate, the awake portions of the system continue to receive a clock signal. While some portions of the clock are turned off, others are left on. Complicated clock gating schemes have been proposed to accomplish this task.
Interrupt signals indicate that the processor should stop its current action and perform an action indicated by the interrupt signal. Therefore, the interrupt signals must eventually get to the processor. However, sometimes multiple interrupt signals are received at almost the same time. These multiple interrupt signals likely have different priority. Further, it may be possible to mask selected interrupt signals. To assess incoming interrupt signals, it has been proposed to send all interrupt signals to a main processor for evaluation. However, this wastes processor resources.